1. Field of the Invention
The present invention relates to an air bag cover for an air bag apparatus installed on a vehicle or the like.
2. Background Information
An air bag apparatus, which is assembled to a steering wheel, an instrument panel, qr the like, is so designed that an air bag is inflated with a gas to expand toward an occupant of the vehicle in the event of a head on collision of the vehicle so as to prevent the forward movement of the occupant, thereby ensuring the safety of the occupant.
The air bag apparatus is provided with an air bag cover which conceals and protects the air bag and the like. Known air bag covers are so constructed that, in the event of a collision of the vehicle, a linear thin-walled portion is broken by being pressed from inside by the air bag which is inflated at that time, allowing the air bag to protrude from an opening thereby formed (Japanese Patent Laid-Open No. 127336/1975 and Japanese Utility Model Publication No. 49887/1983).
However, in order to enhance its outward appearance in design, an air bag cover has in recent years come to be provided with a thin-walled portion which is not composed of one rectilinear groove portion, but, as shown in FIG. 8, there has been proposed an air bag cover 102 provided with an attractive thin-walled portion 100 which is formed by combining a pair of rectilinear horizontal groove portions 100A and a loop-shaped groove portion 100B.
However, in an air bag apparatus 106 shown in FIG. 10 in which an air bag 104 for pressing an air bag cover 102 is accommodated in a folded state as illustrated, at the time when the air bag 104 is inflated, those peripheral portions 104A, 104B of the air bag 104 that are located most closely to the air bag cover 102 first press intermediate portions (portions X and Y and their vicinity in FIG. 8) of the horizontal groove portions 100A of the air bag cover 102. Consequently, maximum strains occur at the intermediate portions of the horizontal groove portions 100A, so that breakage commences at these intermediate portions of the horizontal groove portions 100A.
Such being the case, if a right-hand portion (the right-hand side in FIG. 8) of the air bag cover 102 is taken up as an example, as shown in FIG. 9, the breakage which has occurred at the portion Y which is an intermediate portion of the horizontal groove portion 100A advances as indicated by arrows A and B. However, at a point of intersection between the rectilinear horizontal groove portion 100A and the curvilinear groove portion 100B, the direction of breakage is bifurcated into two directions, one heading in the direction of arrow C and the other heading in the direction of arrow D. Consequently, there is the possibility that a portion Z of the air bag cover 102 surrounded by arrow C and arrow D may be torn off and scattered.